This invention relates to a document handling apparatus and specifically concerns a means and method for automatically moving documents into and out of a position at which they may be copied.
Document handlers separate an individual document from a stack of documents to be copied and move it to an exposure platen where it is registered, held until the required number of copies have been made, and then moved onto an output collection point to be followed by successive documents in the stack. For this purpose the document handling apparatus should provide a convenient and reliable means of maximizing the copy capacity of the machine as well as increasing the quality of registration and copy control over what would be possible with manual operation.
In a generally way, sheet feeding devices for transporting an individual document from a stack of documents to an exposure station are known in the art as shown for example in U.S. Pat. Nos. 3,506,257, 3,674,363, 3,863,912, 3,893,662 and U. K, Pat. No. 1,381,684. The known devices, however, suffer shortcomings in that they do not generally possess the high degree of document control and/or registration capability equal to the high speeds at which machines now operate. Thus, the automatic handler must not only rapidly move the document but must accurately register the document in a specific predetermined copying position or area to assure the production of a complete and visually acceptable copy. For example, if the document is situated on the platen in a skewed or misaligned position within the area, the copy will reflect this same skew or misalignment and may be incomplete and/or unacceptable to the user. If the original is torn or creased it may not be acceptable to the user for a great number of reasons, not the least of which may be unsuitability for subsequent use in a machine or automated processor. The automated document handler must also be able to accept a maximum range of paper or material weights efficiently as documents copied may vary from light weights such as what is known as "onion skin" to very much heavier weights. Another important criteria for an automated document handler is the ability to readily accommodate manual document handling as is necessary when bulky items such as books must be copied. This means the working area or exposure platen must be able to be quickly cleared and be easily accessible to an operator who may have only one page of a book to copy between runs comprising stacks of documents. All of these functions must be performed with a maximum of reliability under wide variations of heat and humidity by a device manufacturable at minimum cost.
While the prior art has in some ways addressed itself to the above points it will be apparent that the solutions have been unduly complex and/or incomplete. For example, several allow compensation for initial manufacturing tolerances and misalignment but do not overcome any inconsistent skew which may occur. Others rely upon readily changeable variables such as timing accuracy and the repeatability of motor braking and lack of slip so that while they may be tuned to provide good results, the effect is temporary.
It was recognized that if a document could be registered against a stop, the number of variables could be reduced; however, it was found that the wide belts used required critical settings of belt tensions and/or allowed only small skew compensations which were unacceptable for some purposes.